Edible wreath-shaped food casings, especially sausage casings

ABSTRACT

Edible wreath shaped food casings are produced by a blow-extrusion method in which the inflated extruded tube is fed onto a series of rotating carrier elements whose peripheral velocity is the same as the rate of discharge of the tube from the extrusion nozzle. The carrier elements may be shaped in a variety of ways but the extruded tube is always led onto the first one tangentially. Lifting guides ensure proper transfer of the tube from one carrier element to the next. The method permits the production of thin-walled casings.

This is a continuation of application Ser. No. 828,487 of Aug. 29, 1977,now abandoned, which was a division of application Ser. No. 647,977 ofJan. 9, 1976, now U.S. Pat. No. 4,081,562, which, in turn, was acontinuation-in-part of application Ser. No. 452,333 of Mar. 18, 1974,now abandoned.

The invention relates to a process and apparatus for the production ofedible wreath-shaped food casings, especially sausage casings.

From German Patent Specification No. 650 526 it is already known toproduce tubes of animal skin fibre material in the form of a continuousspiral which, when cut into individual parts, produces wreath orring-shaped sausage casings. The production of the tubes may be effectedin one of two ways: firstly, by extrusion (for example, using aneccentrically arranged nozzle core) there is produced a straight casingwhich is of irregular thickness about its periphery which, on leavingthe nozzle, bends as a result of the irregularity of width of the nozzlegap. This irregularly thick casing is thus drawn off spirally in uniformcoils, wherein the thicker regions are always subjected to the strongestexpansion. Another way of imparting a spiral shape to the casingconsists of extruding from a correspondingly shaped nozzle, for example,a bevelled nozzle, a tube with a uniform wall thickness which alreadyhas the necessary curvature when it leaves the nozzle, and drawing offthe resulting tube spirally. To wind up spirally the only slightlycurved casing, or to draw off spirally the casing which leaves thenozzle curved, there is provided a spiral roller conveyor. This conveyorconsists of guide rollers which are arranged in concentric coils, and incorresponding layers, around a drive shaft. Some of the guide rollersare driven by the drive-shaft and some are freely rotatable to act assupport rollers. In general, whilst being conveyed in the rollerconveyor, the tube is dried with warm air. For this purpose the rollerconveyor is arranged in a closed drying tunnel. During its transportthrough the roller conveyor and the drying tunnel, the tube may besprayed with water-removing agents, tanning solutions and/orplasticisers, and re-dried.

Such a roller conveyor has considerable disadvantages: firstly, becauseof its many drives, it is a very sensitive device. More significant,however, is the disadvantage which results from the contact between thetube and the guide and support rollers. At these points the tube isthermally damaged because the guide and support rollers assume thetemperature of the drying air (approximately 50° C.) whilst the tubetemperature is substantially lower, at approximately 25° C., as a resultof the evaporating water. To avoid such damage it is necessary to carryout the drying with cooler air, resulting in the drying period beinglonger and necessitating a longer drying path. Even more serious are thefriction problems resulting from the friction between the tube and theguides. As a result of continual milling action at the points of highfriction, material is lost and, consequently, the wall thickness of thetube is reduced. The material rubbed off is deposited on the guides.Owing to the intensive milling effect, the tube has to be extrudedinitially at a corresponding thickness to compensate for the loss inmaterial occurring along the transport path and to ensure that there isan adequate wall thickness and air-tightness in the tube even at the endof the transport path.

To avoid these disadvantages it has already been proposed, in GermanPatent Specification No. 670 552, to dispense with guiding the tubespirally. In this case a tube coil is produced which is not woundspirally but is drawn off continuously in the direction of its axiswithout turning, preferably in a straight line, and is if necessarysimultaneously dried and hardened. This is effected either by causingthe extrusion nozzle to revolve around a transport device which movesforward linearly, in which case the tube coil is formed by theintersection of the revolving nozzle and linearly advancing conveyordevice, or by a process in which the casing is extruded from astationary ring nozzle and is introduced into a guide channel, whichcarries on from the ring nozzle and is preferably curved in asemi-circle running around the extended longitudinal axis of the nozzle,by means of which channel the tube is delivered spirally on a conveyordevice. Such a process, however, is obviously expensive. A revolvingnozzle necessitates expensive sealing means. If, on the other hand, thenozzle remains stationary and the guide channel connected to the nozzlerotates, then again there is undesired friction between the tube and theguide rollers of this guide channel.

In the production of straight sausage casings, it has been proposed toavoid damage to the casing during the transport on the roller conveyorby blowing drying air onto all sides of the casing and to convey it,without there being any contact, suspended on an air cushion.Analagously, in the production of wreath-shaped sausage casingsaccording to German Patent Specification No. 676 320 there is used atubular channel which corresponds to the ring or wreath to be formed.Here the gas outlets are arranged spirally in the wall of the channeland the tube is thus conveyed spirally around the pipe so that it isalways disposed above the gas outlets. According to an improvement ofthis process described in German Patent Specification No. 676 320, thetube does not have to be conveyed spirally around a pipe but is onlycarried or supported from below and transported free-standing in theshape of a continuous coil. To this end the tube inflated with gas isconveyed over a trough adapted to the curvature of the coil, and thesurface of the trough is moved in the direction of circulation of thecoil. The tube has therefore to be supported over only a small part ofthe coil periphery, so that the contact between the coil and astationary support is reduced, thereby also reducing friction to a greatextent. The trough surface preferably consists of adjacently arrangedopen-link chains. This process is, however, best suited for tubes ofvery large bore, since in the case of small diameter tubes, the smallsupporting surface of the trough is not sufficient to guide the coilundamaged through the plant without further support or supportingsurfaces. Instead, the coils of thinner tubes break during transport andtherefore cannot be transported free-standing. In practice, additionaldifficulties occur when transporting tubes of large bore, resulting fromthe construction of the trough surface. It proves very difficult, owingto there being such a small supporting surface, to transport the coilsthrough the plant without trouble in a free-standing condition.

With previously proposed processes and devices it is possible to produceonly relatively thick-walled tubes which, on account of theircomparatively large wall thickness, could hardly be eaten even if thecasing material were in itself edible. As used herein, therefore, ediblecasings shall mean casings which are both composed of edible materialand sufficiently thin, for example, from 8μto 40μ(1μ=10⁻⁴ cm ), to beedible.

It is therefore an object of the invention to provide a method andapparatus for producing a thin-walled and edible wreath-shaped foodcasing.

In the extrusion process of the invention the casing is conveyed, afterleaving the extrusion nozzle, over rotating carrier elements, theperipheral speed of which corresponds to the discharge velocity of theskin from the extrusion nozzle. The required coiling is achieved byconveying the inflated tube around the rotating carrier elements withsuitable lifting members causing transfer from one carrier element tothe next.

Advantageously, the lifting devices comprise rollers, and are preferablyso arranged with respect to the carrier elements that substantially theentire weight of the tube rests on the carrier element, and the liftingrollers are not or not appreciably strained by the weight of the tube.Because the peripheral speed of the carrier elements corresponds to thedischarge speed of the tube from the extruder, relative movement betweenthe extruded skin and the carrier element is avoided so that damagecaused by friction, such as loss of material and the like, is prevented.In addition, the supporting function of the carrier elements reduces thefriction between the tube and the lifting device to a minimum.

The invention accordingly provides a process for the production ofedible, wreath-shaped food casings by means of blow-extrusion and sprialdraw-off of the inflated extruded casing and, if necessary, drying,handening or tanning and/or plasticising of the casing, in which processthe extruded inflated casing is deposited tangentially on peripheralsurfaces of carrier elements rotating at substantially the same speed asthe casing is discharged from the extrusion nozzle, and is transportedfrom one carrier element to the next by means of guides each preferablyin the form of one or more rollers and arranged obliquely to the spiralaxis.

Conveyance of the tube from one carrier element to the next ispreferably assisted by lateral guides, which also preferably compriserollers. When smooth running is achieved, that is to say, when theperipheral speed of the carrier element and the discharge speed of thetube from the extruder agree exactly, friction-between the tube andthese lateral guides is practically nil.

Further details of the process will be apparent from the followingdescription of apparatus according to the invention.

The invention also provides an extrusion apparatus for the production ofedible wreath-shaped food casings, wherein a plurality of rotatablecarrier elements are arranged one behind the other on a driven shaft,the carrier elements being arranged to rotate at substantially the samespeed as the discharge speed of the tube from the extrusion head, thefirst carrier element being arranged to receive the extruded tubetangentially and there being provided at least one lifting devicebetween each adjacent pair of carrier elements for guiding the tubetherebetween.

The shape of the carrier elements is determined substantially by thespiral shape of the tube. Sharp edges or corners, on which the tubemight be damaged, should be avoided. Advantageously, the carrier elementis in the shape of a cylindrical disc. In general, the elements will beplaced, with coupling members, on a common device shaft.

The width of the carrier element, i.e. the supporting surface for thetube, is not critical, but should be at least as large as the width ofthe tube. Preferably, the supporting surface of the carrier element isbroader than the tube so as to allow a certain play for the tube on thecarrier element.

Instead of a cylindrical disc, the or each carrier element may be in theform of a carrier star which rotates around a central axis and has atits arm ends rotatably mounted rollers which carry the casing.

If the casing is dried during transport over the carrier elements, issubsequently moistened again, e.g. by spraying with solutions of tannin,plasticiser and/or dye, and redried, it is subjected to successivelongitudinal shinkages and expansions as a result of drying andre-moistening.

Preferably, the carrier elements are conical, each cone taperingoutwardly in the direction of the spiral axis, that is to say, in thedirection of the next carrier element. As a result of the conicalformation a self-regulating action is produced which avoids slack andstresses. The casing always tends to ride up to the highest point of thecarrier element which, however, is only possible in so far as skinfollows from the previous carrier element. Advantageously a cone of 5°to 25°, preferably 10° to 20° is used.

The guides for lifting the tube from one carrier element to the next areadvantageously adjustably arranged so that the angle formed by thespiral axis with respect to the longitudinal axis of the guide may bealtered. By this means it is possible to control the pitch of the spiralproduced.

Directing the casing onto the next carrier element may be assisted bylaterally arranged low friction guides which are preferably in the formof rollers.

The lifting devices and lateral guide devices preferably comprisestainless steel, desirably coated with Teflon to reduce friction, hardrubber, other plastics materials or wood. The lifting devices and thelateral guides are low friction and advantageously mounted on rollerbearings.

There is practically no friction on the carrier elements, which rotateat substantially the same speed as the discharge speed of the tube fromthe extruder, so that the selection of material for these elements isnot critical. Preferably, however, the conical or cylindrical carrierelements consist of stainless steel which, if necessary, is coated withplastics. Other materials which may be used include wood and plasticsmaterials.

Preferably, the edible skins are produced from animal skin fibrousmaterial (Collagen). In addition, other edible materials, such asalginate, casein and polyvinyl alcohol, may be used. A collagencomposition can be obtained in known manner by treating animal skinsfollowed by a mechanical pulverisation. The edible skins or materialsare also sufficiently thin to be edible and, preferably, from 8μto40μthick.

The casing may be produced by the wet or dry spinning method. In the wetspinning process the casing must first of all be fixed in a coagulatingbath before it is led to the revolving support elements. In the dryspinning process for collagen compositions with drying substancecontents of 6 and 15%, the tube is placed directly on the rotatingcarrier elements after extrusion from the nozzle.

It is, in principle, possible to make a spiral in the described mannerboth with a tube of irregular wall thickness and one with uniform wallthickness. A tube of irregular wall thickness is produced, for example,by extrusion from a nozzle with an eccentric core. As a result of thedifference in wall thickness, such a tube leaves the nozzle alreadysomewhat curved. In just the same way, it is possible to produce a foodcasing of uniform wall thickness--e.g. by means of a double rotatableSaitlings extrusion head in which the core and casing rotate in oppositedirections--and to guide this tube by means of carrier elements andlifting devices according to the invention and so to curve it spirally.In this case, however, it is necessary to put up with the fact that,conditioned by the originally uniform wall thickness, the tube has onits outer side as a result of the relatively marked expansion, asomewhat smaller wall thickness than on the inside of the wreath.

A process for making edible food-casings in accordance with theinvention, and several forms of apparatus in accordance with theinvention, will now be described by way of example with reference to theaccompanying drawings, in which:

FIG. 1 shows a plan view of one form of apparatus in conjunction with adrying channel;

FIG. 2 shows a cross-section through an apparatus similar to FIG. 1 buthaving a different form of carrier element; and

FIG. 3 shows a side elevation of a further form of carrier and transportelements.

Referring to FIG. 1, an extruded collagen tube (1) inflated with a gas,leaves an extruder (2) and is led on to the first of a series ofrotating conical carrier elements (6). The carrier elements (6) withcoupling members, are seated on a carrier shaft (6'). The carrierelements are driven by a carrier shaft (5), with coupling members. Thecarrier shaft (5) is in turn driven by a chain wheel drive (4) by meansof an infinitely variable drive (3). The discharge speed of the extrudedskin is substantially equal to the peripheral speed of the carrierelement (6). Spiral shaping of the skin casing is produced by liftingrollers (7). Although FIG. 1 shows two lifting rollers, a trouble-freetransfer between adjacent carrier elements may also be achieved with onelifting roller. The lifting rollers (7) direct the skin, by reason oftheir inclined position, onto the next succeeding carrier element. Thisguiding is assisted by guide rollers (8), which are arranged laterally.During its passage through this transport device, the skin is subjectedby drying and remoistening to longitudinal shrinkages and expansions.These alterations in length are compensated for by the conicity of thecarrier elements (6). By this arrangement a self-regulating action isproduced which avoids slack and stresses. The arrangement permits theproduction of a very thin-walled spiral-shaped collagen tube suitablefor eating. This advantage arises from the fact that practically norolling friction occurs between the skin and the transport members, anderosion of the material of the collagen tube is therefore avoided.

As shown in FIG. 2, the drying air passes via an air conduit (9) into adrying channel (10), and from this through apertures (11) into the skindrying shaft (12). Used drying air passes through discharge apertures(13) into a chamber from which it is blown into the open air by means ofexhaust fans.

The carrier element shown in FIG. 2 is provided with elevations or ribs,so as to reduce the contact surface between the carrier element and thetube.

The carrier element shown in FIG. 3 takes the form of a carrier starhaving spokes (15), which rotates about the central axis of the carriershaft (5). Arranged on the carrier star (15) are rotatably mountedrollers (14) which carry the skin (1). The lifting rollers (7) and theguide rollers (8) have the same function as in FIGS. 1 and 2.

The following Example illustrates the invention:

From a collagen composition produced in known manner and having acollagen content of 9%, based on dry collagen, there is produced througha nozzle with an eccentrically mounted core a slightly curved tube of 30mm. calibre. The discharge speed of the tube from the extrusion head is0.2 m/sec. The extruded tube, inflated with air, is placed on the firstof 48 conical carrier elements arranged one behind the other on a shaft(for example, as shown in FIG. 1). The shaft with the carrier elementsis driven by means of a chain wheel transmission from an infinitelyvariable drive. Whilst passing the carrier elements, warm air at atemperature of 50° C. is blown in through apertures in the base of aclosed housing surrounding the transport device, and used air escapesthrough apertures in the roof of the housing. The conical carrierelements have a diameter of 130 mm, and the pitch of the cone is 15°.

After passing through the drying chamber, a dried spiral-shaped collagentube with a ring diameter of 150 mm is obtained which corresponds incurvature to a natural skin. This tube is plasticised by spraying with a5% aqueous glycerol solution and then wound on rolls or immediatelyshirred. The rolled up or shirred skin is subsequently hardened byheating for several hours at 70° to 90° C.

The tube may also be hardened by adding a tanning agent to thecomposition or by spraying the tube with solutions of tanningsubstances. Examples of tanning agents which may be used includealdehydes, such as formaldehyde, glutaraldehyde, or glyoxal, or metalsalts such as alum, ferric sulphate, or aluminium sulphate.Advantageously, any excess tanning agent is removed by washing.

Tanning with solutions of tanning substances may be effected beforeand/or during the drying process. Softening of the tube may be effectedby the addition of plasticisers such as glycerol or sorbitol to thecomposition, or by moistening the extruded tube with an aqueous solutionof a plasticiser after hardening and washing.

I claim:
 1. An artificial edible wreath-shaped food casing having a wallthickness in the range of from 8μ to 40μ.
 2. An edible sausage casingaccording to claim 1 and consisting of collagen.
 3. The casing accordingto claim 1 wherein the casing has been extruded and inflatedtangentially onto the surface of a rotating carrier element having aperipheral speed substantially equal to the speed at which the casing isextruded.
 4. The casing according to claim 3 wherein said carrierelement rotates 0.5% to 2% faster than the casing is extruded.
 5. Acasing according to claim 3 wherein the surface of said element has aconical form.
 6. A wreath-shaped sausage casing having a wall thicknessbetween 8μ and 40μ formed by blow extrusion from an extrusion nozzle,the extruded casing having been led in the form of a spiral by extrudingit tangentially onto the peripheral surface of the first of a successionof truncated conical carrier elements, mounted one after another on acommon axis, said carrier elements having been simultaneously rotatedwith a peripheral speed substantially equal to the discharge speed ofthe casing from the extrusion nozzle, and the casing having beenconveyed from one carrier element of the succession to the next with theaid of guide means arranged obliquely to the axis of rotation of saidelements.